It's hard to tell just by looking or even measuring if a shock is blown, since the spring is largely responsible for the ride height.

do the push down test. push down on the each corner and count how many "bounces" it takes before it stops. If that one corner takes more than the others then, it could be worn out or worn out more than the others.

geneally more than 1 cycle = worn shock

1 cycle equals the shock going down then up.